Magnetoresistive Random Access Memory (MRAM) is an emerging technology that may be competitive with prior integrated circuit memory technologies, such as floating gate technology. The MRAM technology may integrate silicon-based electronic components with magnetic tunnel junction technology. A significant element in MRAM is the magnetic tunnel junction (MTJ) where information may be stored. The MTJ stack has at least two magnetic layers separated by a non-magnetic barrier, where a fixed layer has a set magnetic property and a free layer has a programmable magnetic property for storing information. If the fixed layer and the free layer have parallel magnetic poles, the resistance through the MTJ stack is measurably less than if the fixed layer and the free layer have anti-parallel poles, so parallel magnetic poles may be read as a “0” and anti-parallel poles may be read as a “1.” The MTJ stack is typically incorporated into a memory cell, and many memory cells with MTJ stacks art incorporated into a memory bank.
The magnetic properties of the free layer are changed when the memory cell is programmed, where the alignment of the free layer magnetic properties is changed relative to the fixed layer magnetic properties in the programming process. Programming changes the magnetic properties of the free layer and the fixed layer from anti-parallel to parallel, or from parallel to anti-parallel. The programming process typically includes applying a charge across the MTJ stack such that a programming current passes through the MTJ stack. Reductions in the current required to program the MTJ stack improve the overall efficiency of the integrated circuit. The free layer of the MTJ stack has a perpendicular magnetic anisotropy (PMA) value, and higher PMA values decrease the required current to program the free layer. Higher PMA values also produce a lower damping constant, where a lower damping constant is also associated with a reduced current required for programming.
The stability of the permanent magnetic pole in the free magnetic layer degrades as the temperature increases, and the free layer may become demagnetized if the temperature exceeds the Curie temperature for the magnetic material in the free magnetic layer. A demagnetized free layer no longer retains the stored information. Thermal stability of the MTJ stack is related to an energy barrier of the MTJ stack, where higher energy barriers provide greater thermal stability. An energy barrier of the free layer should be sufficiently high to maintain thermal stability at packaging reflow process temperatures and/or at operating temperatures. Changes that increase the PMA values should not reduce the energy barrier to a point where the thermal stability of the free layer is compromised at process or operating temperatures.
Accordingly, it is desirable to provide integrated circuits with magnetic tunnel junctions having higher PMA values and reduced current requirements for reprogramming, as compared to traditional magnetic tunnel junctions, and methods for producing the same. In addition, it is desirable to provide integrated circuits with magnetic tunnel junctions that remain thermally stable as PMA values increase, and methods of producing the same. Furthermore, other desirable features and characteristics of the present embodiment will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.